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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
NASA NTRS2009

Recent Electric Propulsion Development Activities for NASA Science Missions

(The primary source of electric propulsion development throughout NASA is managed by the In-Space Propulsion Technology Project at the NASA Glenn Research Center for the Science Mission Directorate. The objective of the Electric Propulsion project area is to develop near-term electric propulsion technology to enhance or enable science missions while minimizing risk and cost to the end user. Major hardware tasks include developing NASA s Evolutionary Xenon Thruster (NEXT), developing a long-life High Voltage Hall Accelerator (HIVHAC), developing an advanced feed system, and developing cross-platform components. The objective of the NEXT task is to advance next generation ion propulsion technology readiness. The baseline NEXT system consists of a high-performance, 7-kW ion thruster; a high-efficiency, 7-kW power processor unit (PPU); a highly flexible advanced xenon propellant management system (PMS); a lightweight engine gimbal; and key elements of a digital control interface unit (DCIU) including software algorithms. This design approach was selected to provide future NASA science missions with the greatest value in mission performance benefit at a low total development cost. The objective of the HIVHAC task is to advance the Hall thruster technology readiness for science mission applications. The task seeks to increase specific impulse, throttle-ability and lifetime to make Hall propulsion systems applicable to deep space science missions. The primary application focus for the resulting Hall propulsion system would be cost-capped missions, such as competitively selected, Discovery-class missions. The objective of the advanced xenon feed system task is to demonstrate novel manufacturing techniques that will significantly reduce mass, volume, and footprint size of xenon feed systems over conventional feed systems. This task has focused on the development of a flow control module, which consists of a three-channel flow system based on a piezo-electrically actuated valve concept, as well as a pressure control module, which will regulate pressure from the propellant tank. Cross-platform component standardization and simplification are being investigated through the Standard Architecture task to reduce first user costs for implementing electric propulsion systems. Progress on current hardware development, recent test activities and future plans are discussed.

Pencil, Eric J.↗
NASA NTRS1996

Ergonomic Evaluations of Microgravity Workstations

Various gloveboxes (GBXs) have been used aboard the Shuttle and ISS. Though the overall technical specifications are similar, each GBX's crew interface is unique. JSC conducted a series of ergonomic evaluations of the various glovebox designs to identify human factors requirements for new designs to provide operator commonality across different designs. We conducted 2 0g evaluations aboard the Shuttle to evaluate the material sciences GBX and the General Purpose Workstation (GPWS), and a KC-135 evaluation to compare combinations of arm hole interfaces and foot restraints (flexible arm holes were better than rigid ports for repetitive fine manipulation tasks). Posture analysis revealed that the smallest and tallest subjects assumed similar postures at all four configurations, suggesting that problematic postures are not necessarily a function of the operator s height but a function of the task characteristics. There was concern that the subjects were using the restrictive nature of the GBX s cuffs as an upper-body restraint to achieve such high forces, which might lead to neck/shoulder discomfort. EMG data revealed more consistent muscle performance at the GBX; the variability in the EMG profiles observed at the GPWS was attributed to the subjects attempts to provide more stabilization for themselves in the loose, flexible gauntlets. Tests revealed that the GBX should be designed for a 95 percentile American male to accommodate a neutral working posture. In addition, the foot restraint with knee support appeared beneficial for GBX operations. Crew comments were to provide 2 foot restraint mechanical modes, loose and lock-down, to accommodate a wide range of tasks without egressing the restraint system. Thus far, we have developed preliminary design guidelines for GBXs and foot.

Whitmore, Mihriban↗
DOE OSTI2020

Spin-orbit-proximitized ferromagnetic metal by monolayer transition metal dichalcogenide: Atlas of spectral functions, spin textures, and spin-orbit torques in Co/MoSe 2 , Co/WSe 2 and Co/TaSe 2 heterostructures

In this work, the heterostructures composed of an ultrathin ferromagnetic metal (FM) and a material hosting strong spin-orbit (SO) coupling are the principal resource for SO torque and spin-to-charge conversion nonequilibrium effects in spintronics. The key quantity in theoretical description of these effects is nonequilibrium spin density, which can appear on any monolayer of the heterostructure through which the current is flowing as long as the monolayer bands are affected by the native or proximity induced SO coupling. Here we demonstrate how hybridization of wave functions of Co layer and a monolayer of transition metal dichalcogenides (TMDs)—such as semiconducting MoSe 2 and WSe 2 or metallic TaSe 2 —can lead to dramatic transmutation of electronic and spin structure of Co within some distance away from its interface with TMD, when compared to the bulk of Co or its surface in contact with a vacuum. This is due to proximity induced SO splitting of Co bands encoded in the spectral functions and spin textures on its monolayers, which we obtain using noncollinear density functional theory (ncDFT) combined with equilibrium Green function (GF) calculations. In fact, SO splitting is present due to structural inversion asymmetry of the bilayer—i.e., just the presence of the interface—even if SO coupling within TMD monolayer is artificially switched off in ncDFT calculations. However, switching it on makes the effects associated with proximity SO coupling within Co layer about five times larger. Injecting spin-unpolarized charge current through SO-proximitized monolayers of Co generates nonequilibrium spin density over them, so that its cross product with the magnetization of Co determines SO torque. The SO torque computed via first-principles quantum transport methodology, which combines ncDFT with nonequilibrium GF calculations, can be used as the screening parameter to identify optimal combination of materials and their interfaces for applications in spintronics. In particular, we identify heterostructure two-monolayer-Co/monolayer-WSe 2 as the most optimal one, at least in the clean limit.

2-dimensional systems↗
DOE OSTI2015

Establishment and experimental verification of the photoresist model considering interface slip between photoresist and concave spherical substrate

A thickness distribution model of photoresist spin-coating on concave spherical substrate (CSS) has been developed via both theoretical studies and experimental verification. The stress of photoresist on rotating CSS is analyzed and the boundary conditions of hydrodynamic equation are presented under the non-lubricating condition. Moreover, a multivariable polynomial equation of photoresist-layer thickness distribution is derived by analyzing and deducing the flow equation where the evaporation rate, substrate topography, interface slip between liquid and CSS, and the variation of rotational speed and photoresist parameters are considered in detail. Importantly, the photoresist-layer thickness at various CSS rotational speeds and liquid concentrations can be obtained according to the theoretical equation. The required photoresist viscosity and concentration parameters of different photoresist coating thickness under a certain coating speeds can be also solved through this equation. It is noted that the calculated theoretical values are well consistent with the experimental results which were measured with various CSS rotational speeds and liquid concentrations at steady state. Therefore, both our experimental results and theoretical analysis provide the guidance for photoresist dilution and pave the way for potential improvements and microfabrication applications in the future.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Characterization of Ion Implantation and Irradiation Effects in Interface-Dominated Metallic Composites

The candidate structural and fuel cladding materials for the next-generation nuclear power reactors must possess excellent irradiation damage tolerance, and high mechanical and thermal stability that present a challenge for materials design. Here we report an approach to engineer interphase boundaries in metallic composites to achieve superior resistance to void swelling and prevent loss of plastic deformability after irradiation. Model composite systems of face-centered-cubic (Cu) and body-centered-cubic (Nb, Mo or V) metals are used to elucidate the effects of boundary structure and spacing on the damage accumulation and mechanical properties after irradiation. Transmission electron microscopy (TEM) and nano-mechanical testing are used to characterize the irradiation response. A recent development in in situ straining in high-resolution TEM to measure lattice strains and thereby estimate local stresses corresponding to dislocation nucleation and migration is discussed as a capability that in future can enable quantitative characterization of defect interactions in irradiated materials. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2018

Precipitation behavior and phase transformation mechanism of super austenitic stainless steel S32654 during isothermal aging

Highlights: • σ phase formed following a sequence: intergranular, cellular and intragranular. • Cellular σ phase was firstly detected in S32654 aged at 800–900 °C. • Cellular σ growth is controlled by both intergranular and bulk Cr, Mo diffusion. • N-rich zone and Cr diffusion near σ phase induced the nucleation of Cr{sub 2}N. • Local needle-like σ transformed into Cr{sub 2}N and R phase through Cr, Mo diffusion. - Abstract: Thermodynamic calculation as well as microstructure characterization was carried out to investigate the precipitation behavior of super austenitic stainless steel S32654 aged at 700–1100 °C. The corresponding precipitation characteristics and transformation mechanisms of secondary phases were proposed. The results demonstrate that σ phases with various morphologies formed during isothermal aging, and followed a sequence of intergranular, cellular and intragranular with aging temperature. The intergranular σ phase nucleated much faster than the intragranular one due to the lower nucleation energy and higher element diffusion rate at grain boundary. Most intragranular σ phase grew into needle-like shape because of the great difference in mobility of the interfaces formed around it. The cellular σ phase was firstly detected in S32654, and its growth process was successively controlled by intergranular diffusion and then by bulk diffusion of Cr and Mo. Both Cr and Mo bulk diffusion and large needle-like σ phase resulted in the incompleteness of cellular precipitation of σ phase. Another new phenomenon was found that σ phase could induce the precipitation of Cr{sub 2}N ahead of cell boundary, between lamellar σ phases and at the σ/γ interfaces. Meanwhile, local parts of needle-like σ phase gradually transformed into Cr{sub 2}N and R phase through Cr and Mo diffusion from the former to the latters.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Atom probe tomography of intermetallic phases and interfaces formed in dissimilar joining between Al alloys and steel

While Si additions to Al are widely used to reduce the thickness of the brittle intermetallic seam formed at the interface during joining of Al alloys to steel, the underlying mechanisms are not clarified yet. The developed approach for the site specific atom probe tomography analysis revealed Si enrichments at grain and phase boundaries between the θ (Fe{sub 4}Al{sub 13}) and η (Fe{sub 2}Al{sub 5}) phase, up to about ten times that of the concentration in Al. The increase in Si concentration could play an important role for the growth kinetics of the intermetallic phases formed for example in hot-dip aluminizing of steel. - Highlights: •Si additions to Al reduce thickness of intermetallic seam in joining with steel. •Approach developed for the site specific APT analysis of the intermetallic seam •Si enrichment at grain and phase boundaries possibly affects growth of intermetallics.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Aerosolized ZnO nanoparticles induce toxicity in alveolar type II epithelial cells at the air-liquid interface

The majority of in vitro studies characterizing the impact of engineered nanoparticles (NPs) on cells that line the respiratory tract were conducted in cells exposed to NPs in suspension. This approach introduces processes that are unlikely to occur during inhaled NP exposures in vivo, such as the shedding of toxic doses of dissolved ions. ZnO NPs are used extensively and pose significant sources for human exposure. Exposures to airborne ZnO NPs can induce adverse effects, but the relevance of the dissolved Zn2+ to the observed effects in vivo is still unclear. Our goal was to mimic in vivo exposures to airborne NPs and decipher the contribution of the intact NP from the contribution of the dissolved ions to airborne ZnO NP toxicity. We established the exposure of alveolar type II epithelial cells to aerosolized NPs at the air-liquid interface (ALI), and compared the impact of aerosolized ZnO NPs and NPs in suspension at the same cellular doses, measured as the number of particles per cell. By evaluating membrane integrity and cell viability 6 and 24 hours post exposure we found that aerosolized NPs induced toxicity at the ALI at doses that were in the same order of magnitude as doses required to induce toxicity in submersed cultures. In addition, distinct patterns of oxidative stress were observed in the two exposure systems. These observations unravel the ability of airborne ZnO NPs to induce toxicity without the contribution of dissolved Zn2+ and suggest distinct mechanisms at the ALI and in submersed cultures.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2012

The epitaxial growth of (1 1 1) oriented monocrystalline Si film based on a 4:5 Si-to-SiC atomic lattice matching interface

Highlights: ► A monocrystalline Si film was demonstrated by XRD to epitaxially grow on the 6H-SiC substrate. ► A 4:5 Si-to-SiC lattice matching structure was observed at the Si/SiC interface. ► The calculated value of the actual lattice mismatch is only 0.26%. ► Defects can be effectively reduced at the 4:5 Si-to-SiC lattice matching Si/SiC interface. -- Abstract: Due to a huge lattice mismatch of about 20% theoretically existing between SiC and Si, it is difficult for growing monocrystalline Si/SiC heterojunction to realize the light control of SiC devices. However, based on a 4:5 Si-to-SiC atomic lattice matching interface structure, the monocrystalline Si films were epitaxially prepared on the 6H-SiC (0 0 0 1) substrate by hot-wall chemical vapor deposition in our work. The film was characterized by X-ray diffraction analysis with only (1 1 1) orientation occurring. The X-ray rocking curves illustrated good symmetry with a full width at half maximum of 0.4339° omega. A 4:5 Si-to-SiC atomic matching structure of the Si/6H-SiC interface clearly observed by the transmission electron microscope revealed the essence of growing the monocrystalline Si film on the SiC substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Role of Protein-Water Interface in the Stacking Interactions of Granum Thylakoid Membranes—As Revealed by the Effects of Hofmeister Salts

The thylakoid membranes of vascular plants are differentiated into stacked granum and unstacked stroma regions. The formation of grana is triggered by the macrodomain formation of photosystem II and light-harvesting complex II (PSII-LHCII) and thus their lateral segregation from the photosystem I—light-harvesting complex I (PSI-LHCI) super-complexes and the ATP-synthase; which is then stabilized by stacking interactions of the adjacent PSII-LHCII enriched regions of the thylakoid membranes. The self-assembly and dynamics of this highly organized membrane system and the nature of forces acting between the PSII-LHCII macrodomains are not well understood. By using circular dichroism (CD) spectroscopy, small-angle neutron scattering (SANS) and transmission electron microscopy (TEM), we investigated the effects of Hofmeister salts on the organization of pigment-protein complexes and on the ultrastructure of thylakoid membranes. We found that the kosmotropic agent (NH 4 ) 2 SO 4 and the Hofmeister-neutral NaCl, up to 2 M concentrations, hardly affected the macro-organization of the protein complexes and the membrane ultrastructure. In contrast, chaotropic salts, NaClO 4 , and NaSCN destroyed the mesoscopic structures, the multilamellar organization of the thylakoid membranes and the chiral macrodomains of the protein complexes but without noticeably affecting the short-range, pigment-pigment excitonic interactions. Comparison of the concentration- and time-dependences of SANS, TEM and CD parameters revealed the main steps of the disassembly of grana in the presence of chaotropes. It begins with a rapid diminishment of the long-range periodic order of the grana membranes, apparently due to an increased stacking disorder of the thylakoid membranes, as reflected by SANS experiments. SANS measurements also allowed discrimination between the cationic and anionic effects—in stacking and disorder, respectively. This step is followed by a somewhat slower disorganization of the TEM ultrastructure, due to the gradual loss of stacked membrane pairs. Occurring last is the stepwise decrease and disappearance of the long-range chiral order of the protein complexes, the rate of which was faster in LHCII-deficient membranes. These data are interpreted in terms of a theory, from our laboratory, according to which Hofmeister salts primarily affect the hydrophylic-hydrophobic interactions of proteins, and the stroma-exposed regions of the intrinsic membrane proteins, in particular—pointing to the role of protein-water interface in the stacking interactions of granum thylakoid membranes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Atomic layer deposition of Al{sub 2}O{sub 3} on germanium-tin (GeSn) and impact of wet chemical surface pre-treatment

GeSn is quickly emerging as a potential candidate for high performance Si-compatible transistor technology. Fabrication of high-ĸ gate stacks on GeSn with good interface properties is essential for realizing high performance field effect transistors based on this material system. We demonstrate an effective surface passivation scheme for n-Ge{sub 0.97}Sn{sub 0.03} alloy using atomic layer deposition (ALD) of Al{sub 2}O{sub 3}. The effect of pre-ALD wet chemical surface treatment is analyzed and shown to be critical in obtaining a good quality interface between GeSn and Al{sub 2}O{sub 3}. Using proper surface pre-treatment, mid-gap trap density for the Al{sub 2}O{sub 3}/GeSn interface of the order of 10{sup 12} cm{sup −2} has been achieved.

36 MATERIALS SCIENCE↗